Local Seattlite here. I can't speak properly to anything east of the Cascades, but I'll speak to those I'm very familiar with by responding to your list directly:
Snoqualmie Valley TrailLove this trail. It's just beautiful and very safe. Ride it all the time on our Surly Midnight Specials. It's all packed gravel, if you have 32's or wider you'll be just fine. If you're trying to connect multiple trails, this one dives into Duvall and ends there. To connect to any of the other trails, the best way is to peel off in Carnation and hit up a very popular riding route on the main road through town. Heading south wraps you around into Redmond (very pretty riding with only one grinder up and over into Redmond), specifically on East Lake Sammamish Road which will bring you to the East Lake Sammamish Trail/Sammamish River Trail/Burke-Gilman Trail.
East Lake Sammamish TrailThis stretches from Issaquah up into MaryMoor Park in Redmond where it connects directly to the Sammamish River Trail. The route I mentioned from the above trail will drop you down onto the road that this trail parallels. It's mostly paved, with a bit of it being packed gravel. They're actively working on paving a bit more of it every year it seems. If there is construction, the road that this trail follows (East Lake Sammamish Parkway) is quite safe, a super popular riding route that the vast majority of cyclists ride rather than the trail since it's easier (way less stops, there are a lot of driveways that go down to waterfront homes that have right of way) and much smoother.
(I actually have never ridden the Issaquah trail you mentioned so I can't speak to how the two may connect, but I do know they're not very close to one another so it'd be a bit of road riding to connect).
Sammamish River Trail/Burke-Gilman TrailAs mentioned above, the Sammamish River Trail connects from Redmond, around Lake Washington where it turns into the Burke-Gilman to bring you right into Seattle. It's all fully paved. It dips by the University of Washington, through Fremont and ending in Ballard.
Fun fact: The recent completion of the new 520 bridge features a damn fine bridge trail that stretches from UW, across the bridge, and into the Bellevue/Kirkland border. Some safe road riding will connect you onto the East 520 bridge trail that dips down into Redmond connecting directly with the Sammamish River Trail, giving you a couple options for getting to Seattle. Though if you're wanting to avoid hills, take the normal SRT-Burke route
Ship Canal TrailThis is a paved trail that begins in South Lake Union and parallels the Burke along the canal. To get to it from the Burke, you'll take the Burke into Fremont, peel off to cross over the canal via the Fremont Bridge, with the Ship Canal Trail just underneath. The trail itself will dump you on a dedicated cycling path alongside the road in the Magnolia area, where you can safely connect to the Elliot Bay Trail.
Elliot Bay TrailThis paved trail will bring you from the Magnolia area and over to the Seattle waterfront/downtown proper. A bunch of it was redone thanks to Expedia. It's a beautiful ride with full views of the entire waterfront stretch. The start of it is pretty narrow as it squeezes between some private property, but it won't last long.
Hope that helps